Controllable frequency magnetically coupled multivibrator



Dec. 14, 1965 w. E. DAMON CONTROLLABLE FREQUENCY MAGNETICALLY COUPLED MULTIVIBRATOR Filed Aug. :1. 1961 d fj/f7d 6 25:2520)? BY ATTORNEY United States Patent "ice 3,223,945 CONTRULLABLE FREQUENCY MAGNETKCALLY COUPLED MULTTVTBRATOR Wayne E. Damon, Martinsvillc, 1nd, assignor to General Motors (Zorporation, Detroit, Mich, a corporation of Delaware Filed Aug. 21, 1961, Ser. No. 132343 169 Ciairns. (til. 331-113) This invention relates to magnetically coupled multivibrators and more particularly to an improved device for controlling the output frequency.

One form of the prior art regarding magnetically coupled multivibrators comprises a circuit similar to a conventional free running multivibrator circuit wherein two transisters are connected in push-pull .and are operated by regenerative feedback from feedback windings disposed on the same saturable core as are the primary windings. The disadvantage of such a circuit is that by using one high remanence core for controlling the switching of the two transistors the operation must depend upon knee to knee saturation of the core. In addition, such a circuit has the disadvantage in that the output voltage will vary with changes in frequency since the input voltage must change in order to produce a resulting frequency change. The circuit has a limitation in the maximum operation frequency that can be obtained since by relying on flux changes in the knee to knee saturation of the core there will be resultant core losses limiting the practical upper frequency limit.

The disadvantages and limitations of the above circuit have resulted in further improvements in the more recent development of the prior art. Circuits have been developed which utilize two high remanence cores thereby permitting switching operation which does not depend upon knee to knee saturation of one core to complete the cycle. Instead, each core need saturate at only one knee and reset during the alternate half cycle. Thus one core may be driven to saturation by regenerative feedback from the switching transistor which it is controlling While the inactive core is simultaneously being reset. The reset of the inactive core is accomplished by inductive coupling inasmuch as the secondary winding on the active core is coupled to the secondary winding on the inactive core in such a manner that the current induced in the former also flows in the latter in a direction to reset the inactive core. In addition thereto, the amount of reset is controlled by utilizing a control current and control windings to vary the level of reset applied to the inactive core. However, circuits which operate as described inherently have circulating currents in the control circuit thus requiring a low impedance control source.

In accordance with this invention, a magnetically coupled multivibrator circuit is provided having two high remanence cores in which the requirement for a low impedance source is circumvented by utilizing conductive coupling instead of inductive coupling for obtaining reset of the inactive core. The conductive coupling is obtained by providing parallel connected primary windings on each of the two high remanence cores permitting current flow simultaneously in the saturating direction in the primary winding wound on one core and in the resetting direction in the primary winding wound on the second core.

A more complete understanding of this invention may be had from the detailed description which follows taken from the accompanying drawings in which:

FIGURE 1 is a schematic circuit diagram of one embodiment of the invention;

FIGURE 2 is a schematic circuit diagram of another embodiment of the invention.

Referring now to the drawings and particularly to FTG- URE 1 there is shown an illustrative embodiment of the 3223345 Patented Dec. 14, 1365 invention. The controllable frequency magnetically coupled multivibrator comprises two high remanence cores 1i) and 12 and two switching transistors 14 and 16. The core 1&1 has wound thereon primary windings 18 and 20, a feedback winding 22, a control winding 24 and a bias winding 26. The core 12 has wound thereon primary windings 23 and 30, a feedback winding 32, a control winding 34 and a bias winding 36. The transistor 14 comprises a base 38, a collector 4i) and an emitter 42. The transistor 16 comprises a base 44, a collector 46 and an emitter 48. The emitters 42 and 43 are connected in common to the negative terminal of a battery 50. The primary windings 18 and 28 are conneced in parallel between the positive terminal of the battery 50 and the collector 46 of the transistor 16. The primary windings 2t) and 39 are connected in parallel between the positive terminal of the battery Sit and the collector iii of the transistor 14. A voltage divider circuit comprising resistances 52 and 54- provides forward bias to the transistors 14- and 16 via a resistor 56 and the feedback windings 22 and 32 connected to the bases 38 and 44, respectively. The bias windings 26 and 36 are connected together in series and form a loop circuit with a bias voltage supply at and a resistor 62. The sense of the windings on cores 1G and 12 is indicated by heavy dots. The output of the multivibrator circuit may be taken across terminals 64 and 66 connected to the common terminals of the parallel connected primary windings 18 and 28 and 2t and 34 respectively.

An understanding of the operation of the multivibrator circuit shown in FIGURE 1 may be had from the following description. Assume that the transistor 14 has just become conductive and that the transistor 16 is in its non-conductive state. The transistor 14 will continue to conduct as determined by the regenerative feedback voltage induced in the feedback winding 22 until core 1t saturates at which time the voltage induced in the feedback winding '22 will suddenly drop to zero. The flux level in the saturating core 13 will drop to its residual value thereby inducing a slight voltage in the feedback winding 22 which will be of a polarity to apply a negative voltage to the base 38 driving transistor 14 further into cut off. At the same time, a slight regenerative feedback voltage will be induced in the feedback winding 32 of such a polarity to apply a slight positive voltage to the base 44 permitting transistor 16 to conduct. The transistor 16 will continue to conduct until the core 12 saturates at which time the cycle will begin anew.

Considering the half cycle during which the transistor 14- is conducting, the voltage from the battery source 50 is applied across the parallel connected primary windings 211 and 31} such that current will flow in the primary winding 20 in a direction to saturate the core 14 and in the primary winding 30 in a direction to reset the core 12. Thus reset of core 12 is obtained through conductive coupling of the parallel connected primary windings 20 and 36. In a like manner, during the period in which transistor 15 is conducting and the transistor 14 is nonductive current will flow through the primary winding 23 in a direction to saturate the core 12 and in the primary winding 18 in a direction to reset the core 19. An output taken across the terminals 64 and 66 will be respfionsive to the switching action of the transistors 14 and 1 The frequency of the magnetically coupled multivibrator circuit in FIGURE 1 is dependent upon the resetting action of the cores 1% and 12, The resetting can be varied by changing the magnitude and direction of the current flowing in a control loop comprising the current control means 53 and the control windings 24 and 34. For example, it the current in the control loop is in a counterclockwise direction it will aid the reset in cores and 12 and thus decrease the frequency of the multivibrator. However, if the current in the control loop is in a clockwise direction it will inhibit the reset in cores 10 and 12 and thus increase the frequency of the multivibrator. A lower limit of frequency can be established by utilizing a bias control loop including the bias voltage source 60 in series with bias windings 26 and 36 providing a predetermined level of saturation of cores 10 and 12.

Another embodiment of the invention is shown in the circuit in FIGURE 2 which includes two high remanence cores 100 and 102 and two switching transistors 104 and 166. The core 10%) has wound thereon a primary winding 103, a control winding 110, a feedback winding 112 and a bias winding 114. The core 102 has wound thereon a primary winding 116, a control winding 118, a feedback winding 120 and a bias winding 122. The transistor 104 comprises a base 124, a collector 126 and an emitter 128. The transistor 106 comprises a base 130, a collector 132 and an emitter 134. The emitters 128 and 134 are connected in common to the positive terminal of a battery 136. The primary windings 108 and 116 are connected together in parallel between the collector 126 of transistor 104 and the collector 132 of transistor 106. A voltage divider circuit comprising resistors 133 and 140 provides forward bias to the transistors 104 and 106 via the resistor 142, and the parallel connected feedback windings 112 and 120 connected to the bases 124 and 130, respectively. The bias windings 114 and 122 are connected in series and form a loop circuit with a resistor 144, the battery 136 and a bias control resistor 146. The control windings 110 and 118 are connected in series and form a loop circuit with a current control means 148.

A non saturating power transformer 150 has wound thereon a center tapped primary winding 152 comprising an upper half 154 and a lower half 156. The negative terminal of the battery 136 is connected to the center tap 151 of primary winding 152, The collector 126 of transistor 104 is connected to the outer terminal of the upper half 154, whereas the collector 132 of transistor 106 is connected to the outer terminal of the lower half 156 of the primary winding 152. The sense of the windings on cores 100 and 102 is indicated by the heavy dots. The output of the multivibrator may be taken across terminals 160 and 162 of an output winding 158 wound on the non-saturating power transformer 150.

The operation of the circuit in FIGURE 2 is similar to that as described in conjunction with the circuit in FIGURE 1. Assume that the transistor 104 has just become conductive and that the transistor 106 is in its non conductive state. The transistor 104 will continue to conduct as determined by the regenerative feedback voltage induced in the feedback winding 112. A voltage will be applied to the upper half 154 of the primary winding 152 of a value approximately equal to the battery voltage 136. Through transformer action an induced voltage will appear in the lower half 156 of the primary winding 152 and thus a net voltage of approximately twice the battery voltage 136 will appear across the primary winding 152. This voltage will in turn be applied across the parallel connected primary windings 103 and 116. Current flowing through the primary windings 108 and 116, respectively, will be in a direction to saturate the core 100 and to reset the core 102. When the core 100 becomes saturated, the regenerative feedback voltage induced in the feedback winding 112 will suddenly drop to zero with a resultant loss in conductivity of transistor 104, The flux level in core 100 will then drop to its residual value thereby inducing a slight voltage in the feedback winding 112 and applying a positive voltage to the base 124 driving the transistor 104 further into cut off. At the same time, a slight regenerative feedback voltage will be induced in the feedback winding 120 applying a negative voltage to the base 130 permitting the transistor 106 to become conductive. Transistor 106 Will 4 continue to conduct until the core 102 saturates and the cycle begins anew.

The frequency of the voltage appearing across the terminals 160 and 162 is dependent upon the resetting action of the cores and 102. The resetting action can be controlled by varying the magnitude and direction of the current flowing through the control loop comprising the control windings and 118 connected together in series with the control current source 148. If the current in the control loop is in a counterclockwise direction it will aid the reset action of cores 100 and 102 and thus decrease the frequency of the multivibrator. However, if the current in the control loop is in a clockwise direction the resetting action of cores 100 and 102 will be inhibited with a resulting increase in the frequency of the multivibrator. A lower limit of operating frequency can be established by utilizing a bias control loop including the bias voltage source 136 in series with bias windings 114 and 122, a control resistor 146 and a resistor 144 providing a predetermined level of saturation of cores 100 and 102.

Although the description of this invention has been given with respect to a particular embodiment, it is not to be construed in a limiting sense. Numerous variations and modifications within the spirit and scope of the invention will now occur to those skilled in the art. For a definition of the invention, reference is made to the appended claims.

I claim:

1. A magnetically coupled multivibrator comprising a first, second, third and fourth primary windings, said first and second windings being connected in parallel and mounted on first and second cores respectively, said third and fourth windings being connected in parallel and mounted on said first and second cores respectively, a source of energy, first and second on-off switching means alternately connecting said source across said first and second parallel connected windings and said third and fourth parallel connected windings respectively to alternately drive one of said cores to saturation while simultaneously resetting the other of said cores, and output means responsive to the frequency of operation of said switching means.

2. A magnetically coupled multivibrator comprising a first and second plurality of windings disposed on first and second saturable cores respectively, each of said pluralities of windings including first and second windings, said first windings being connected in parallel, said second windings being connected in parallel, a source of energy, first and second on-otf switching means alternately connecting said source to said first and second windings respectively to alternately drive one of said cores to saturation while simultaneously resetting the other of said cores, and output means responsive to the frequency of operation of said switching means.

3. A magnetically coupled multivibrator comprising a first and second plurality of windings disposed on first and second saturable cores respectively, each of said pluralities of windings including at least first and second windings, said first windings being connected in parallel, said second windings being connected in parallel, a control circuit comprising first and second control windings connected in series and disposed on said first and second cores respectively, current control means connected across said first and second control windings, a source of energy, first and second on-otf switching means alternately connecting said source across said first and second windings respectively to alternately drive one of said cores to saturation while simultaneously resetting the other of said cores whereby equal and opposite voltages are induced in said control circuit, and output means responsive t0 the frequency of operation of said switching means.

4. A magnetically coupled multivibrator comprising first and second alternately conducting transistors, each of said transistors having a collector, a base, and an emitter electrode, first and secondary primary windings disposed on first and second cores respectively, third and fourth primary windings disposed on said first and second cores respectively, said first and second windings connected in parallel and said third and fourth windings connected in parallel, first and. second feedback windings disposed on said first and second cores respectively and connected between the emitter and base electrodes of said first and second transistors respectively, a source of energy, said first and second transistors adapted to alternately connect said first and second parallel connected windings and said third and fourth parallel connected windings respectively across said source to alternately drive one of said cores to saturation while simultaneously resetting the other of said cores, and output means responsive to the frequency of operation of said transistors.

5. A magnetically coupled multivibrator comprising a first and second plurality of windings disposed on first and second saturable cores respectively, each of said pluralities of windings including a first and second primary winding, a bias winding, and a feedback winding, said first primary windings being connected in parallel, said second primary windings being connected in parallel, said bias windings being connected in series, bias control means connected across said bias windings to provide a predetermined level of saturation of said first and second cores, a pair of transistors each having a collector, a base, and an emitter electrode, said emitter electrodes connected in common, one of said feedback windings being connected across the emitter and base electrodes of one of said transistors, the other of said feedback windings being connected across the emitter and base of the other of said transistors, a source of power, said first and second transistors alternately connecting said primary windings across said source through the emitter and collector electrodes to alternately drive one of said cores to saturation while simultaneously resetting the other of said cores, and output means responsive to the frequency of operation of said transistors.

6. A magnetically coupled multivibrator comprising a first and second plurality of windings disposed on first and second saturable cores respectively, each of said pluralities of windings including a first and second primary winding, a bias winding, and a feedback winding, said first primary windings being connected in parallel, said second primary windings being connected in parallel, said bias windings being connected in series, bias control means being connected across said bias windings to provide a predetermined level of saturation, a control circuit comprising a control winding mounted on each of said cores, said control windings being connected in series, current control means connected across said control windings, a pair of transistors each having a collector, a base, and an emitter electrode, said emitter electrodes connected in common, one of said feedback windings being connected across the emitter and base electrodes of said first transistor, the other of said feedback windings being connected across the emitter and base of said second transistor, a source of power, said first and second transistors alternately connecting said first and second primary windings across said source through the emitter and collector electrodes to alternately drive one of said cores to saturation while simultaneously resetting the other of said cores whereby equal and opposite voltages are induced in said control circuit, and output means responsive to the frequency of operation of said transistors.

7. A magnetically coupled multivibrator comprising first and second transistors, each having a collector, a base, and an emitter electrode, a first and a second primary winding disposed on first and second saturable cores respectively, a third and a fourth primary winding disposed on said first and second cores respectively, a feedback winding disposed on said first and second saturable cores respectively, said first and second primary windings being connected in parallel, said third and fourth primary winding being connected in parallel, said feedback windings being connected between the base and emitter electrodes of said first and second transistors respectively, said first and second transistors alternately connecting said source across said first and second parallel connected windings and said third and fourth parallel connected windings to drive one of said cores to saturation while simultaneously resetting the other of said cores, and output means responsive to the frequency of operation of said transistors.

8. A magnetically coupled multivibrator comprising a plurality of first and second windings disposed on first and second saturable cores respectively, each of said pluralities of windings including a primary winding, a bias winding, and a feedback winding, said primary windings connected in parallel, said bias windings connected in series, a control circuit comprising a control winding mounted on each of said cores, current control means connected across said control windings, a pair of transistors each having a collector, a base, and an emitter electrode, said emitter electrodes connected in common, one of said feedback windings being connected across the emitter and base electrodes of one of said transistors, the other of said feedback windings being connected across the emitter and base of the other of said transistors, 21 source of power, means connecting said bias winding in series across said source to provide a predetermined level of saturation of said first and second cores, a nonsaturable power transformer having first and second primary windings and a secondary winding disposed thereon, said source connecting said first and second transformer primary windings acros the emitter and collector electrodes of said first and second transistors, respectively, the collector electrodes of said transistors being connected respectively to common terminals of said parallel connected primary windings to alternately drive one of said cores to saturation while simultaneously resetting the other of said cores whereby equal and opposite voltages are induced in said control circuit, output means connected to the secondary winding of said power transformer and responsive to the frequency of operation of said transistors.

9. A magnetically coupled multivibrator comprising a pair of saturable cores, a primary winding, a feedback winding and a control winding disposed on each of said cores, said primary windings connected in parallel, said feedback windings connected in parallel, said control windings connected in series, current control means connected across said control windings, a source of energy, first and second transistors having an emitter, base and collector electrode; a non-saturable power transformer having a center tapped primary winding and a secondary winding, said source being connected between said center tap and the emitters of said transistors, the end terminals of said center tapped primary winding being connected respectively to the common terminals of said parallel connected primary windings, the collector electrodes of each of said transistors being connected respectively to the common terminals of said parallel connected primary windings, said transistors conducting alternately to drive one of said cores to saturation while simultaneously resetting the other of said cores whereby equal and opposite voltages are induced in said control circuit, output means connected to the secondary winding of said power transformer and responsive to the frequency of operation of said transistors.

it). A magnetically coupled multivibrator comprising a pair of saturable cores, a control circuit comprising a control winding disposed on each of said cores, current control means connected in series with said control winding, primary winding means disposed on each of said cores, said primary winding means being connected in parallel, a source of energy, first and second alternately conductive electronic switching means connecting said source to said parallel connected primary winding means to provide separate paths of current flow from said source, each of said current paths including primary windings disposed on both of said cores, the current flow through said primary windings driving one of said cores to saturation while resetting the other of said cores and inducing equal and opposite voltages in said control circuit and output means responsive to the frequency of operation of said switching means.

References Cited by the Examiner UNITED STATES PATENTS Hubbard 331113 Uchrin et al 331113 Van Allen 331113 Berman 331113 Eno et a1. 331113 Samusenko 331-113 Rochelle 331-113 ROY LAKE, Primary Examiner. 

10. A MAGNETICALLY COUPLED MULTIVIBRATOR COMPRISING A PAIR OF SAUTRABLE CORES, A CONTROL CIRCUIT COMPRISING A CONTROL WINDING DISPOSED ON EACH OF SAID CORES, CURRENT CONTROL MEANS CONNECTED IN SERIES WITH SAID CONTROL WINDING, PRIMARY WINDING MEANS DISPOSED ON EACH OF SAID CORES, SAID PRIMARY WINDING MEANS BEING CONNECTED IN PARALLEL, A SOURCE OF ENERGY, FIRST AND SECOND ALTERNATELY CONDUCTIVE ELECTRONIC SWITCHING MEANS CONNECTING SAID SOURCE TO SAID PARALLEL CONNECTED PRIMARY WINDING MEANS TO PROVIDE SEPARATE PATHS OF CURRENT FLOW FROM SAID SOURCE, EACH OF SAID CURRENT PATHS INCLUDING PRIMARY WINDINGS DISPOSED ON BOTH OF SAID CORES, THE CURRENT FLOW THROUGH SAID PRIMARY WINDINGS DRIVING ONE OF SAID CORES TO SATURATION WHILE RESETTING THE OTHER OF SAID CORES AND INCUDING EQUAL AND OPPOSITE VOLTAGES IN SAID CONTROL CIRCUIT AND OUTPUT MEANS RESPONSIVE TO THE FREQUENCY OF OPERATION OF SAID SWITCHING MEANS. 